This is a proposal to study the membrane mechanisms which control cellular activity in the vertebrate retina. With newly developed techniques the detailed electrical properties of the membranes for each type of retinal neuron can be defined. From these studies the ionic systems responsible for the electrical properties can be inferred. The inferrences can be tested directly by newly-developed methods of ionic substitution. Synaptic interactions can be controlled and modified by the use of synaptic blocking agents. From these studies we should be able to describe cellular function in terms of a sequence of membrane events including synaptic modulation of specific ionic permeability which affects membrane potential, which modulates transmitter release. Understanding the interplay between different cell types at sites of synaptic interaction will provide a fundamental understanding of information processing in the retina in terms of activity at the membrane level.